Production of high density compacts



Jan. 25, 1966 A. F. MARSHALL 3,231,373

PRODUCTION OF HIGH DENSITY GOMPACTS Filed Oct. 15, 1962 5 line F64N/f MARSHALL Attorneys United States Patent 3,231,373 PRGDUCTEQN 0F HHGH DENSlTY CQMPACTS Alec F. Marshall, Solihull, England, assignor to Agricola Metals Limited, London, England, a British company Filed Oct. 15, 1962, Ser. No. 230,546 Claims priority, application Great Britain, Oct. 13, 1961, 36,880/ 61 i3 Claims. (l. 75-214) The present invention is concerned with improvements in or relating to the production of high density compacts from powder compacts of lower density. The process is particularly but not exclusively useful with increasing thickness of product from about 0.1 inch upwards and is applicable to powdered materials in general.

It is known to compact metallic and non-metallic powders by placing the powders in a channel-shaped container and compressing them by means of a single punch having a fiat pressing surface parallel to the surface of the powder and a pressing surface either angled to or continually curved downwardly to the fiat pressing surface. This process may produce a compact of between 60% and 98 of the theoretical solid density depending on the limitations imposed by such variables as the compacting load applied, the material being processed and by the thickness of the finished product. Such a process is described for example in Iowder Metallurgy, 1960, No. 5, pp. 32- 44. in processes of this type the punch is brought down onto the powder, after which it is raised clear of the powder and the powder advanced from the angled end of the punch towards the fiat section by a distance which depends upon the angularity of the inclined surface of the punch and the initial depth and compression of the pow der. The cycle may then be repeated. By providing support for the compact as it is produced and continuous- 1y feeding powder into the container continuous lengths of such compacts can be obtained.

it has now been found that powder compacts having unexpectedly high densities and low porosities can be obtained by compacting lower density compacts with an led punches.

The invention accordingly provides a process for the production of high density compacts in which a low density compact, preferably one of 60-70% theoretical density, is subjected to cyclic compactions with at least one punch, each such punch having part of its pressing surface substantially parallel to the surface of the low density compact and the remaining part of such pressing surface at an angle to said first-mentioned part, the said angled pressing surface being inclined away from the surface of the compact, the compact being moved relative to the punch or punches between each compaction.

According to a modification of the invention said pressing surface is curved away from the surface of the compact.

FIG. 1 is a longitudinal section of a compact being subjected to compression by two punches;

FIG. 2 is a transverse section along the line IIlI in FIG. 1;

FIG. 3 is a longitudinal section of a first compression step using a single punch;

FIG. 4 is a longitudinal section of the compression step applied in the reverse direction following the compression illustrated in FIG. 3;

FIG. 5 is a longitudinal section of a first compression step applied using a single punch;

FIG. 6 is a longitudinal section of a compression step in the same direction following the compression step illustrated in FIG. 5;

PEG. 7 is a longitudinal section through a compact being compressed by two punches acting on opposite sides of the same section of the compact;

3,231,373 Patented Jan. 25, 1966 FIG. 8 is a longitudinal section through a compact being compressed by two punches acting on opposite sides of different sections of the compact; and

FIG. 9 is a view similar to FIGS. 4 and 5 but showing a die having a curved portion.

The process of the present invention may be applied to low-density compacts formed from any powders known to be suitable for subjection to powder metallurgical processes. The process may, for example, be applied to ceramic compacts and to cermets. It is however particularly applicable to metal compacts, especially those formed from pure nickel, austenitic stainless steel and low alloy steel powders.

The present process is particularly applicable in the reduction of products the first thickness of which exceeds 0.1 inch.

The angle between that part of the pressing surface substantially parallel to the surface of the low density compact (hereinafter referred to as the horizontal pressing surface) and that part at an angle thereto (hereinafter referred to as the angled pressing surface) is preferably at least 3 and desirably between 5 and 13. One or more punches may be used in the process and the angle need not ce the same in each punch.

Vvhcre the low density compact is subjected to two compactions in the present process, it is generally advantageous in terms of punch load and product density to perform the second compaction with a punch whose angled portion makes a greater angle with the surface or" the compact than is the case with the punch used in the first compaction.

The movement of the compact between each compression may be in either direction parallel to that surface of the punch which is paral el to the axis of the compact, and may if desired be reversed after each compression. In a preferred modification of the process the compact is moved away from the punch after each compression. The distance by which it is moved is not critical. In general this distance depends upon the length of the punch and the angle between the angled and horizontal pressing surfaces. The greater the angle and the shorter the punch the less is the maximum distance by which the compact may be moved after each compression.

in one modification of the process of the invention the low density compact 'is supported in such a way that it can be compressed between two punches each acting in diametrically opposite directions on the compact. The punches may act simultaneously or consecutively. In the case of an elongated compact a series oil such pairs of punches may be used. Each pair of punches may act on the same section of the compact or they may be displaced from each other to act on different or overlapping sections of the compact.

The low density compacts to which the process or" the present invention may be applied, may be prepared by any of the conventional methods used for compaction of powde s, or any specific methods known for the con1- paction oi the powders of particular materials. Conventional methods for the compaction of metal powders in clude, for example, placing the powder in a rubber bag within a perforated steel cylinder and subjecting it to isostatic pressure in a closed container filled with a fluid; mixing the powder with a wax-like substance and extruding it through an orifice, after which the wax is removed and the powder retains the shape produced by the extrusion operation; or containing the powder in a rigid die cavity subjecting it to pressure by one or more movable unches.

In a preferred modification of the process of the inven tion the low density compact is formed by subjecting the powder to cyclic compaction using an angledpunch of the same type as that used afterwards to increase the density of the compact but preferably of a lower angle. Densitied green compacts, preferably in the form of strip may thus be formed, having a density in the range of 80% to 98% of that theoretical-1y obtainable.

In a preferred variation of this method of forming the low density compact, the powder is subjected to ultrasonic vibrations while it is being fed into the container in which it will be compacted. The preferred frequency of the vibrations used depends upon the individual blend of particle size and the specific gravity of the powder being compacted. The ultrasonic vibrations may be applied, for example, by rapid oscillation at a suitable frequency and small controlled amplitude of the compacting punch, or by attaching a source of vibration to the wall or base of the channel containing the powder.

In another preferred modification of the process of the present invention a metal compact formed after initial compaction of powder by any of the conventional methods, but preferably by compaction using an angled punch and with powders subjected to ultrasonic vibrations, may be heated to an elevated temperature, preferably a temperature above that required for recrystallisation of the metal concerned, so that work-hardening of the powder due to further compaction is minimised, and held at this temperature during the further compaction. The desired temperature should be attained before any appreciable deformation of the low density compact occurs. Heat may be applied by any convenient method, one suitable method being electric resistance heating, an electric current being passed through the compact. The passage of an electric current also tends to improve the cohesion of the metal particles and the mechanical strength of the compact produced. Alternatively heat may be applied by induction methods, or by local inclusion in a suitable type of furnace.

In the case of compacts formed, either partly or wholly, from metals which oxidise easily, or from the fine powders which may also tend to oxidise, it is preferable to subject either the powder or the low density compact to a heattreatment in a reducing atmosphere or in a neutral atmosphere such as argon or helium, or in a vacuum to reduce oxide films or remove volatile oxides. Such treatment is generally known as a presintering operation. It has been found that when the present process is performed while the compact is so heated such a treatment improves the operation of the process enabling a higher density to be obtained than without it.

It has been found that the density of metal compacts using the process of the present invention can be increased by as much as 35 percent.

The application of the process of the present invention to a low density metal compact is illustrated diagrammatically in the accompanying drawings in which:

In the figures, C is a compact, P, P and P are angled punches, arrows E, E and E indicate the direction in which the compression force is applied by the punches, A and B are marked points on the compact. D is a container for the compact and S is a supporting surface for the compact. FIGURES 1 and 2 illustrate the compaction of a low density compact C to form a high density compact using two punches, P and P In FIG. 1 the angle a is the angle between the angled pressing surface and the horizontal pressing surface of the punch P and the angle 9 is the angle between the angled pressing surface and the horizontal pressing surface of the punch P The punches P and P are applied to the surface of the compact C with compression forces E and E respectively. In between each compression step the compact is moved in the direction shown by arrow F.

FIGURE 2 illustrates the relative positions of punch P compact C and the container D when punch P has been raised after a compression step and before the compact has been moved.

FIGURES 3 and 4 illustrate a modification of the invention in which a single punch is used and the compact is turned through an angle of between compression steps as shown by the marked points A and B.

FIGURES 5 and 6 illustrate a modification of the invention in which a single punch is used and the compact is moved in the direction shown by the arrow F for a distance x between compression steps.

FIGURE 7 illustrates a modification of the invention in which two punches P and P are applied to the same section of the compact C at the same time.

In FIG. 8 the two punches P and P are applied to different sections of the compact C at the same time, each being opposed by a fixed surface S.

FIGURE 9 illustrates a further embodiment wherein the punch P having the parallel bottom surface portion common with the other embodiments but wherein the adjacent portion of the punch is smoothly curved upward- 13 as shown.

I claim:

I. The method of producing high density compacts from low density compacts formed from powders comprising metaliic powders, comprising the steps'of: supporting said low density compact against a surface; cyclically reciprocating a punch against said compact to compress the same against said surface, a portion of said punch being substantially paraliel to said supporting surface and an adjacent portion being inclined thereto and extending from an edge of said one portion in an oblique direction away from said supporting surface; and cyclically moving said compact relative to said punch, between successive reciprocations there-of, in a direction to .position an uncompressed portion of said compact under said punch; and heating said compact to a temperature of at least that required for recrystallization of said metal during said cyclic compression.

2. The method of claim 1 wherein said compact is formed from a readily oxidizable metallic powder and wherein said temperature is maintained while said method is performed in a non-oxidizing atmosphere.

3. The method of producing high density compacts from low density compacts formed from powders comprising metallic powders, comprising the steps of: supporting said low density compact against a surface; cyclically reciprocating a punch against said compact to compress the same against said surface, a portion of said punch being substantially parallel to said supporting surface and an adjacent portion being inclined thereto and extending from an edge of said one portion in an oblique direction away from said supporting surface; and cyclically moving said compact relative to said punch, between successive reciprocations thereof, in a direction to position an uncompressed portion of said compact under said punch.

4. The method of claim 3 wherein said adjacent portion of said punch is curved.

5. The method of claim 3 wherein said low density compact has a density of from 60% to 70% of the theoretical maximum density.

6. The method of claim 3 wherein said compact is formed of a material selected from the group consisting of nickel powder, austenitic stainless steel powder and low alloy stainless steel powder.

'7. The method of claim 3 wherein the angle between said parallel and adjacent portions of said punch is at least 3.

8. The method of claim 3 wherein the angle between said parallel and adjacent portions of said punch is between 5 and 13.

9. The method of claim 3 wherein the compact is moved away from the punch after each compression.

10. The method of claim 3 wherein said supporting surface is defined by a second punch having portions corresponding to and opposed to said recited portions.

11. The method of claim 10 wherein the adjacent portion of said second punch forms an angle with its parallel portion greater than the corresponding angle of said first punch.

12. The method of claim 3 in which said low density compact is formed by cyclic compaction of a powder with a punch of the type defined.

13. The method of claim 3 including the step of subjecting said compact to ultra-sonic vibrations While being compressed.

References Cited by the Examiner UNITED STATES PATENTS 2,289,787 7/1942 Kaschke et a1 264-111 2,333,271 11/1943 Paterson 29-4205 2,384,215 9/ 1945 Toulmin.

2,398,719 4/1946 Rasmussen.

6 2,661,499 12/1953 James et a1. 264-280 2,735,757 2/1956 Zapf 75-05 2,746,741 5/1956 Naeser 266-5 2,842,440 7/1958 Nachtman et a1. 75-214 XR 2,917,821 12/1959 Fritsch 29-4205 2,994,917 8/1961 Fritsch 264-111 3,071,805 1/1963 Merkle 264-120 3,158,474 11/1964 Andersen et a1. 75-223 XR FOREIGN PATENTS 1,275,568 10/1961 France.

ALEXANDER H. BRODMERKEL, Primary Examiner.

M. R. DOWLING, P. E. ANDERSON,

Assistant Examiners. 

1. THE METHOD OF PRODUCING HIGH DENSITY COMPACTS FROM LOW DENSITY COMPACTS FORMED FROM POWDERS COMPRISING METALLIC POWDERS, COMPRISING THE STEPS OF: SUPPORTING SAID LOW DENSITY COMPACT AGAINST A SURFACE; CYCLICALLY RECIPROCATING A PUNCH AGAINST SAID COMPACT TO COMPRESS THE SAME AGAINST SAID SURFACE, A PORTION OF SAID PUNCH BEING SUBSTANTIALLY PARALLEL TO SAID SUPPORTING SURFACE AND AN ADJACENT PORTION BEING INCLINED THERETO AND EXTENDING FROM AN EDGE OF SAID ONE PORTION IN AN OBLIQUE DIRECTION AWAY FROM SAID SUPPORTING SURFACE; AND CYCLICALLY MOVING SAID COMPACT RELATIVE TO SAID PUNCH, BETWEEN SUCCESSIVE RECIPROCATIONS THEREOF, IN A DIRECTION TO POSITION AN UNCOMPRESSED PORTION OF SAID COMPACT UNDER SAID PUNCH; AND HEATING SAID COMPACT TO A TEMPERATURE OF AT LEAST THAT REQUIRED FOR RECRYSTALLIZATION OF SAID METAL DURING SAID CYCLIC COMPRESSION. 